The RRM1 gene has been known for its role as the regulatory subunit of ribonucleotide reductase (RR). We have discovered novel functions for RRM1. It suppresses carcinogen-induced lung tumorigenesis. RRM1 also suppresses tumor progression as demonstrated by decreased cellular migration and invasion in vitro and suppression of metastasis formation in a syngeneic mouse model resulting in increased animal survival. In patients with NSCLC, overall survival (OS) and disease-free survival (DFS) are substantially longer for those with high levels of expression as compared to those with low levels of expression. We had found that ERCC1 expression was likewise significantly associated with OS and DFS, and these data were recently confirmed in a very large independent dataset by a separate group of investigators using standard immunohistochemistry (IHC). In terms of its impact on therapy, RRM1 is the major cellular determinant of chemotherapeutic efficacy for gemcitabine. We have demonstrated this directly in vitro through genetic manipulation of RRM1 expression and in vivo through showing an inverse correlation between RRM1 expression and patients' response to gemcitabine/carboplatin chemotherapy. In addition, we observed a similar but less convincing association between ERCC1 expression and tumor response. Finally, we have completed a single institution phase II trial in patients with advanced NSCLC, where the decision on a chemotherapy doublet was based on tumoral RRM1 expression (whether or not gemcitabine was used) and ERCC1 expression (whether or not platinum was used). The outcome of patients on the trial was extremely encouraging with a 1-year survival of 59%. Most recently, we found a strong and convincing correlation between tumoral RRM1 and ERCC1 expression. In our latest analysis on an association between prognosis and expression of both genes, it was the group of patients with high expression of both genes that had a favorable outcome after surgical resection. This group accounts for 30% of all patients with early-stage NSCLC. These results are the basis for our hypothesis that RRM1 is an important regulator of proliferation, survival, and therapeutic efficacy in NSCLC. The primary focus of this project is to integrate RRM1 into current clinical decision-making, to understand the mechanism of coordinate RRM1 and ERCC1 expression, and to generate tools required for optimization of RRM1-directed therapeutic interventions.